In general, a small-sized camera module is mounted in a mobile terminal such as a smartphone. The lens driving device has an auto-focusing function of automatically performing focusing for capturing a subject (hereinafter referred to as “AF (Auto Focus) function”), and a shake-correcting function (hereinafter referred to as “OIS (Optical Image Stabilization) function”) of optically correcting shake (vibration) upon capturing an image to reduce the irregularities of the image (for example, PTL 1).
A lens driving device having the auto-focusing function and the shake-correcting function includes an auto-focusing driving part (hereinafter referred to as “AF driving part”) for moving the lens part in the light axis direction, and a shake-correcting driving part (hereinafter referred to as “OIS driving part”) for swaying the lens part in a plane orthogonal to the light axis direction.
The AF driving part includes, for example, an auto-focusing coil part (hereinafter referred to as “AF coil part”) disposed at a periphery of the lens part, an auto-focusing magnet part (hereinafter referred to as “AF magnet part”) separated from the AF coil part in the radial direction, and an elastic supporting part (for example, a leaf spring) configured to elastically support an auto focus movable part (hereinafter referred to as “AF movable part”) including the lens part and the AF coil part with respect to an auto focus fixing part (hereinafter referred to as “AF fixing part”) including the AF magnet part for example. By moving the AF movable part in the light axis direction with respect to the AF fixing part by utilizing a driving force of a voice coil motor composed of the AF coil part and the AF magnet part, automatic focusing is performed. It is to be noted that the AF fixing part may include the AF coil part, and the AF movable part may include the AF magnet part.
The OIS driving part includes, for example, a shake-correcting magnet part (hereinafter referred to as “OIS magnet part”) disposed in the AF driving part, a shake-correcting coil part (hereinafter referred to as “OIS coil part”) separated from the OIS magnet part, and a supporting part configured to support a shake correction movable part (hereinafter referred to as “OIS movable part”) including the AF driving part and the OIS magnet part with respect to a shake correction fixing part (hereinafter referred to as “OIS fixing part”) including the OIS coil part. By swaying the OIS movable part in a plane orthogonal to the light axis direction with respect to the OIS fixation part by utilizing a driving force of a voice coil motor composed of the OIS magnet part and the OIS coil part, shake correction is performed (so-called barrel shift system). The OIS magnet part can also serve as the AF magnet part, and with such a configuration, the size and the height of the lens driving device can be reduced. In addition, a suspension wire is employed as a supporting part configured to support the OIS movable part with respect to the OIS fixing part, for example.
Preferably, the diameter of the suspension wire is small in view of increasing the sensitivity of the OIS driving part (hereinafter referred to as “OIS sensitivity”). When the diameter of the suspension wire is small, however, the risk of rupture with an impact of dropping or the like is high. In addition, since the suspension wire is easily deflected in this case, the OIS movable part cannot be translated (the lens part is tilted), and the tilt characteristics in shake correction are degraded. The tilt characteristics indicate the parallelism of the OIS movable part in shake correction, and the tilt characteristics are represented by the inclination angle of the OIS movable part in movement of the lens part. In this manner, when the diameter of the suspension wire is reduced to increase the OIS sensitivity, the reliability of lens driving device is sacrificed.